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>Inotify support on Linux (instantaneous reports, no I/O load)</TITLE
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><H1
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><A
NAME="FINOTIFY"
>5.21. Inotify support on Linux (instantaneous reports, no I/O load)</A
></H1
><P
> The Linux kernel offers an
interface — called <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>inotify</I
></SPAN
> — which
allows an application to obtain
change notifications for files and directories, if the application
has registered <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>watches</I
></SPAN
> for the files and directories
it is interested in.
</P
><P
> As of version 3.0, <SPAN
CLASS="APPLICATION"
>samhain</SPAN
> optionally
can use the <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>inotify</I
></SPAN
> interface.
The advantage of this is twofold:
First, it is not neccessary to perform
regular filesystem scans to detect file changes, i.e. the I/O load is
drastically reduced. And second, changes can be reported immediately,
thus allowing faster responses.
</P
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>Please note</B
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><TD
> </TD
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><P
> Your system may be configured with a too low default for
the maximum inotify watches per user. You can see the default
with:
</P
><P
> <B
CLASS="COMMAND"
>cat /proc/sys/fs/inotify/max_user_watches</B
>
</P
><P
> You can change the default temporarily (i.e. until reboot) with:
</P
><P
> <B
CLASS="COMMAND"
>echo 1048576 /proc/sys/fs/inotify/max_user_watches</B
>
</P
><P
> You can change the default permanently by placing the following
line in <TT
CLASS="FILENAME"
>/etc/sysctl.conf</TT
> (this will take effect
at the next reboot):
</P
><P
> <B
CLASS="COMMAND"
>fs.inotify.max_user_watches=1048576</B
>
</P
><P
> Alternatively, <SPAN
CLASS="APPLICATION"
>samhain</SPAN
> can be configured
to reset the value by itself on startup (see example configuration
below).
</P
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><B
>Full scans</B
></TH
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> </TD
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><P
> (1) On startup, <SPAN
CLASS="APPLICATION"
>samhain</SPAN
> will perform
a full scan, first to set the inotify watches, and second to
recover changes that happened after initialisation of the baseline
database, but before starting the file check.
</P
><P
> (2) The kernel will queue inotify events. If the queue overflows
because there are too many events in too short a time, the application
will be notified. In this case, <SPAN
CLASS="APPLICATION"
>samhain</SPAN
>
will automatically trigger a full scan to recover lost
file system changes.
</P
><P
> (3) Finally, even if inotify is enabled,
<SPAN
CLASS="APPLICATION"
>samhain</SPAN
> will still honour the configured
intervals or schedules for full scans. If you want to rely only on
inotify, you may want to configure a very large interval for
filesystem checks, e.g. 'SetFilecheckTime = 315360000' (10 years).
</P
><P
> Note that currently, <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>directories</I
></SPAN
> specified
via wildcard patterns can only be detected in a full scan if they
appear newly in the filesystem (unless of course the parent directory
is monitored anyway). Wildcard patterns for <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>files</I
></SPAN
>
are checked every 10 seconds.
</P
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CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN3213"
>5.21.1. Example configuration</A
></H2
><PRE
CLASS="PROGRAMLISTING"
> [Inotify]
#
# Activate (default is off)
#
InotifyActive = yes
# Optionally set the maximum number of watches allowed per user.
# (default is leave as is). To see the default, use:
# cat /proc/sys/fs/inotify/max_user_watches
#
InotifyWatches = 1048576
</PRE
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